let minus = document.querySelector('#minus');
let plus = document.querySelector('#plus');
let output = document.querySelector('#output');

minus.addEventListener('click', function () {
  let sum = Number(output.innerHTML) - 1;
  if (sum >= 0) output.innerHTML = sum;
});

plus.addEventListener('click', function () {
  let sum = +output.innerHTML + 1;
  output.innerHTML = sum;
});
